The present invention relates to a color image recording apparatus for recording color images by exposure of a photosensitive recording medium to color-separated images through mask members.
There has been proposed a color image recording apparatus with a monochromatic laser beam printer coupled to its upper portion, as disclosed in U.S. patent application Ser. No. 07/255,342 filed on Oct. 11, 1988 by Toshio Sakai et al. The proposed color image recording apparatus records a color image by employing three primary mask members which are produced by the monochromatic laser beam printer.
The color image recording apparatus includes a positioning or registering device having a feed belt in the form of an endless sheet made of PET (polyethylene terephthalate). The feed belt serves to electrostatically attract a mask member, which has been delivered from the monochromatic laser printer, to its lower surface, and feed the attracted mask member. A charging brush for electrostatically charging the feed belt is disposed near the feed belt. A resist roller is held against the lower surface of an upstream end of the feed belt, and a chute for guiding the mask member into a position between the feed belt and the resist roller is positioned upstream of the feed belt and the resist roller. The color image recording apparatus also includes an exposure device disposed above the positioning unit and having red, green, and blue filters. The exposure device is movable along the feed belt for scanning the mask member positioned by the positioning unit. A continuous photosensitive recording medium, which is disposed below the positioning unit, is closely held against the lower surface of the feed belt with the mask member therebetween when the photosensitive recording medium is to be exposed to light passing through the mask member. A pressure developing unit for holding the exposed photosensitive recording medium and a color developer sheet against each other under pressure to develop an image on the color developer sheet is located downstream of the positioning unit.
The color image recording apparatus operates as follows: A mask member produced by and delivered from the monochromatic laser beam printer is fed through the chute into the position between the feed belt and the resist roller, and electrostatically attracted to the lower surface of the feed belt which is electrostatically charged by the charging brush. The photosensitive recording medium is then closely held against the feed belt with the mask member sandwiched therebetween. The exposure device is energized and moved to scan the mask member so that an image carried on the mask member is transferred to the photosensitive recording medium. This process is repeated to transfer images of three primary mask members by successively exposing the photosensitive recording medium to light passing through red, green, and blue filters. A colored latent image is now formed on the photosensitive recording medium. Thereafter, the photosensitive recording medium is fed into the pressure developing unit in which the photosensitive recording medium and a color developer sheet are held against each other under pressure and heated to form a developed colored image on the color developer sheet.
Since the feed belt is resilient, it has been difficult to hold the photosensitive recording medium and each mask member intimately against each other while in contact with the feed belt. For holding the photosensitive recording medium and the mask member more fully, it is necessary to increase the tension of the feed belt. If the tension of the feed belt is to be increased, however, a belt roller for driving the feed belt and a frame which supports the belt roller have to be increased in mechanical strength. Therefore, the belt roller and the frame tend to be heavy and large in size. Moreover, there is a demand for a light-weight feed belt as it needs to be moved for positioning or registering the mask members.
The feed belt of the positioning unit is moved in a horizontal plane by a moving mechanism comprising a rack and a pinion. The moving mechanism includes a guide member for slidingly guiding the rack. The accuracy with which the feed belt is moved is however low because of lost motion or backlash between the rack and the guide member. In order to eliminate the backlash, it is necessary to increase the dimensional accuracy of various components of the positioning unit, and hence the cost of manufacture of the positioning unit will become prohibitively high. Furthermore, the rack and pinion mechanism inherently suffers from backlash between the rack and the pinion, with the result that the feed belt moved with poor accuracy. Any means for eliminating such backlash has been employed in the earlier color image recording apparatus.
Another brush or the like for dusting off the surface of the feed belt is also held in contact with the feed belt. Inasmuch as the feed belt is made of PET and low in hardness, however, the surface of the feed belt is liable to get scratched or otherwise damaged by this brush and the charging brush. If the feed belt is damaged, its transparency is lowered, and the feed belt cannot be used for a long period of time. Since the damaged feed belt is lower in electric insulation, it cannot be sufficiently electrically charged by the charging brush, and hence cannot well attract the mask member.
In the case where the mask member is of low insulation resistance, when the mask member touches the feed belt of the positioning unit, the mask member may be electrically charged by the electrostatically charged feed belt. When the mask member is electrically charged, it is attracted by the chute or other members while it is being delivered into the positioning unit. The mask member may be stopped by the chute or other members to which it is attracted, and therefore may not properly be fed to the feed belt. There has heretofore been not available a suitable means for removing electrostatic charges from the charged mask member.
Each mask member bears a positioning or registering mark printed on its leading end and detectable by a sensor mounted on a sensor support bar that is positioned underneath the positioning unit. The mask member is positioned or registered in place by the positioning unit when the leading end of the mask member is inserted between the feed belt and the sensor support bar and the positioning mark is detected by the sensor. If the leading end of the mask member is curved downwardly due to humidity or the like before it reaches the sensor support bar, then the leading end of the mask member may not properly be inserted between the feed belt and the sensor support bar, and hence the positioning mark may not be detected by the sensor.